Project Abstract: Despite recent advances in the antibiotic therapy and intensive care, bacterial infections and sepsis remain widespread problems in critically ill patients, annually claiming > 225,000 victims in the U.S. alone. The pathogenesis of sepsis remains obscure, but is partly mediated by bacterial toxins (e.g., lipopolysaccharide, LPS), which stimulate macrophages/monocytes to sequentially release early (e.g., TNF and IFN-?), intermediate (e.g., the Serum Amyloid A, SAA), and late (e.g., HMGB1 and histones) pro-inflammatory mediators. Our seminal discovery of HMGB1 as a late mediator of lethal systemic inflammation (LSI) (Science, 285: 248-51, 1999) has prompted the investigation of various early cytokines (e.g., IFN-?) and liver- derived acute-phase proteins (e.g., fetuin-A and SAA) in the regulation of HMGB1 release. To search for other endogenous HMGB1 regulators, we systematically monitored the dynamic changes of circulating HMGB1 and other proteins in normal healthy subjects versus septic patients, and found a negative correlation between levels of circulating HMGB1 and tetranectin (TN), a plasminogen-binding protein implicated in binding plasminogen (PLMG) to activate the plasmin (PLM)-dependent fibrinolysis. Furthermore, we have generated preliminary data that the highly purified recombinant TN dose-dependently attenuated the LPS/SAA-induced HMGB1 release, but specifically stimulated the release of several neutrophil-attracting chemokines (CXCL1 and CXCL5) by primary human monocytes. In animal models of lethal endotoxemia and sepsis (induced by cecal ligation and puncture, CLP), circulating TN levels were time-dependently decreased; whereas the supplementation with highly purified recombinant TN conferred a significant protection. These exciting findings raised several important questions regarding the intricate mechanisms underlying the TN-mediated inhibition of HMGB1 release, as well as its significant protection against LSI. Accordingly, we propose to test: 1) the novel hypothesis that TN divergently regulates HMGB1 release and neutrophil-attracting chemokine expression through distinct mechanisms (Aim 1); 2) the under-appreciated role of TN in LSI by using gene knockout or supplementation with recombinant TN or TN-specific peptide agonists (Aim 2); and 3) the novel mechanisms by which TN or TN-specific peptide agonists affect the outcome of LSI (Aim 3). Collectively, these proposed studies will improve our understanding of the pathophysiology of endotoxemia and sepsis, and help to identify novel therapeutic strategies for the treatment of sepsis and other inflammatory diseases.